The present invention relates to a satellite communication system between small earth stations, in particular, relates to a satellite communication system using hybrid modulation which may monitor operation status of those earth stations in such a satellite communication system. The present invention is used for transmit power control by a large relay earth station such that rain attenuation due to rain attenuation sustained by small earth stations is compensated for.
A small earth station has been used currently in a satellite communication system, following the use of a large communication satellite, the development of digital communication systems, and/or the development of communication components. In a satellite communication system with a plural small earth stations, it is desirable to monitor the operation status of each earth station in a unified manner by a monitor station for effective and reliably operation of the communication system, and/or unattended operation of a small earth station. The monitored information is also used for transmitting power control by a monitor station for compensating for rain attenuation at small earth station side.
The transmission of monitor information has been carried out through a communication channel itself, or through a specific control channel dedicated for transmission of monitor information. For instance, when a circuit is a TDMA circuit, said monitor information, including bit error rate, C/N (carrier to noise power ratio) of receive signal et al, is inserted in a preamble portion of the TDMA signal. When the circuit handles continuous signal, the signal is transmitted by using frame structure of signal, and said monitor information is inserted at a header portion of the frame.
However, those monitor information transmission systems have the disadvantages that the signal processing is complicated, and the large amount of attachments to a conventional communication system are necessary for the transmission of monitor information, since the structure of a communication circuit itself must be changed.